[boost] Re: [optional] new assignmet semantic and references

From: David Abrahams (dave_at_[hidden])
Date: 2005-03-01 10:43:02

"Fernando Cacciola" <fernando_cacciola_at_[hidden]> writes:

> This is not the way assignment of reference types work in C++:
>
> ra = rb ; // The value of 'a' referenced by 'ra' is changed, not the 
> reference itself.
> cout << a ; Prints 789
>
> This error in the way optional<T&> treated assignment of reference types was 
> pointed out by Joel de Guzman long ago when he started using Optional in 
> Spirit. However, at the time, Joel explicitely asked me not to change this 
> and keep the current rebinding semantics in order to minimize any impact in 
> Spitit itself (which certainly has, o had, a much larger user base).
>
> If I change the code now to use T's operator=(), assignment of optional<T&> 
> will have a _radically_ different semantics. A correct one, that's for sure, 
> but end user code might be fundamentally impacted.

You might want to consider whether it makes sense to change the
semantics only for non-reference types.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com